Radiation treatment is referred to as a procedure in which radiation is applied to a target region or volume of interest (VOI) and is an inclusive term that includes both low dose treatments (e.g., radiotherapy) and high dose treatments (e.g., radiosurgery). Radiation treatments may require a high degree of precision and, thus, a system with components that can meet such requirements. One example of such system is the CyberKnife® system made by Accuray Incorporated of Sunnyvale, Calif. The CyberKnife® system is an image guided, robotic-based radiation treatment system. This system has a radiation source coupled to a robotic arm having multiple degrees of freedom that allows the radiation source to move and operate within a volume of space also referred to as a workspace. The multiple degrees of freedom allow the robot to conceivably achieve an infinite number of positional possibilities within its operating envelope. Allowing this type of movement provides flexibility but it may lead to other challenges. First, it creates a challenge for the treatment planning system by making it difficult to select beams for treatment. Secondly, it would allow the robot to travel anywhere within its workspace, but it must also recognize obstructions in which to avoid. These challenges are solved by creating specific paths that the robot must follow during treatment delivery.
The specific paths may be created by defining some specific workspace areas, for example, head and body. The workspace is generally a geometrical shape centered about a centroid of the geometrical shape which may be designed according to the location of the target. For example, the workspace can take the shape of a sphere or an ellipse. The workspace is generally defined by a source-to-axis distance (SAD), the distance between a collimator in a radiation source and the target. For example, in medical applications, a workspace for the anatomical head region may be defined by two spheres with SADs of approximately 650 mm and approximately 800 mm. In another example, a workspace for the neck may be defined by SADs ranging from about 650 mm to about 750 mm. This workspace is limited to the volume defined by the multiple concentric spheres with radii approximately ranging from about 650 mm to about 750 mm centering about the target in the neck region. When treating tumors in the rest of the body, the CyberKnife® system uses SAD values of approximately 900 to approximately 1000 mm. This approach compresses the workspace, but there are still an infinite number of positions where the robot could stop on the surfaces of these volumes. So, to address this, arbitrary positions are created along the surface of the sphere where the robot can stop to deliver treatments. Specifically, the workspace is characterized by a finite number of positions, referred to as spatial nodes, in the volume of space between the surface area of the smallest concentric sphere (650 mm) and the surface area of the largest concentric sphere (750 mm). These substantially uniformly distributed spatial nodes in a workspace are collectively known as the superset of nodes. However, only a partial number of this superset of nodes is used for radiation treatment with a particular CyberKnife® system that is installed at a site (e.g., hospital). Each site (e.g., hospital) at which a CyberKnife® system is installed may have a unique partial number of nodes that are defined by the geometry of the treatment room. A typical installation of a CyberKnife® system may have, for example, approximately 100 to approximately 130 of such nodes.
The partial number of nodes, within the superset of nodes, for a particular installation site provides a safe, or a collision-free, path of travel for the robotic arm mounted radiation source. This collision-free path of travel is obtained by arranging, in sequence, a partial number of nodes within the superset of nodes, so that the radiation source will not encounter any obstruction when traversing through the node sequence. This partial number of nodes within the superset of nodes is known as the template nodes. This safe and collision-free plan of travel is composed of direct paths between template nodes that are free of obstruction. The safe and collision-free path of travel is determined by a computation intensive off-line simulation and real-life testing in a CyberKnife® system treatment room. This safe and collision-free path of travel is formed from a pre-defined order or sequence of the template nodes and is unique to a treatment installation site or a particular treatment configuration.
Determination of the safe and collision-free plan of travel by a computer intensive off-line simulation process and testing with a real system is time consuming because of the large possibilities of safe or collision-free paths within a given superset of nodes and the arbitrary nature of the path selection process. An algorithm simulates a radiation source moving from a home position to a first spatial node, followed by a second spatial node, then a third, and a fourth etc., until an object or obstruction is encountered between spatial nodes. Upon encountering an obstruction, the algorithm eliminates that path by removing that destination spatial node, and applying the sequential number of that removed node to a next non-mapped spatial node. The simulation continues to reiterate and map spatial nodes to generate an obstruction free travel path that takes the radiation source back to the home position while eliminating spatial nodes that lead to collisions with obstructions or spatial nodes that are redundant. Ultimately a safe or collision-free path is established and determined by a set of spatial nodes. This set of spatial nodes is the template nodes, where each template node is numbered in sequence and if the radiation source follows the template nodes in order of the sequence, no obstruction will be encountered.
Each template node is assigned a number in the sequence so the radiation source travels along the path according to the order of the sequence. A treatment plan is generated from input parameters such as beam position and beam orientation that are available to the system based on the template nodes. The treatment plan specifies quantities such as the directions and intensities of the applied radiation beams, and the durations of the beam exposure. Treatment plans typically do not require delivery of the radiation beams at all of the available template nodes. However, due to the existing configuration of path traversal, even though the radiation source only needs to delivery radiation at a partial set of the template nodes, the radiation delivery source still has to visit all template nodes in an order defined by the sequence in the safe or collision-free plan of travel in order to ensure that the robotic arm mounted radiation source does not collide with the patient or another object. Having to cycle through the entire set of template nodes along a known safe or collision-free path increases the amount of time that is required to provide treatment.